Is it important for me to buy another model another than nikon d3000?

How to make the picture good like nikon d90? Is it something to do with lens? Because mine is basic len 18-55. Or i have to change another lens to take good picture? What's the most important to take picture? I'm still beginner.

If you are having problems creating amazing photos with your D3000, buying a better camera will NOT help.

You have to learn the fundamentals of photography to assure good images from ANY camera

You can use any camera, dSLR or not, to make a good looking picture. You just have to know exactly what you are doing. You already have a capable camera and a decent all-around lens. Here is what you need.

http://keerok-photography.blogspot.com/2011/05/what-are-best-settings-for.html

In your case, skills.

I've done some pretty good work with a 18-55 on a nikon d50.

Find great moment and great object (it is depend on your interest), it can take with any kind of camera, even you just use cellphone's camera, practise makes perfect, buying an expensive Nikon doesn't make you a great photographer, it makes you a Nikon owner, and your first 10, 000 images are your worst.

In other word: you must know your gear, explore all of the ability, the menus and so on, don't be afraid to make an experiment, follow flickr community to get some reference… Good Luck